Hello,

I have an old rear projection television that I would like to take
apart and use the frame for another project. The television has not
been plugged in since the year 2000. Do I still need to discharge
capacitors even though it hasn't seen AC in 4 years? Could anyone
tell me how long it would take on average for the caps to discharge
by themselves?

Thanks in advance.

"Steve" wrote in message
news
Hello,

I have an old rear projection television that I would like to take
apart and use the frame for another project. The television has not
been plugged in since the year 2000. Do I still need to discharge
capacitors even though it hasn't seen AC in 4 years?

YES

Could anyone
tell me how long it would take on average for the caps to discharge
by themselves?

it dosent matter assume they are charged just as you should assume a gun is
loaded when you handel it.


Thanks in advance.


never trust a bleeder resistor... it could be open

"Ross Herbert" bravely wrote to "All" (25 Aug 04 12:12:46)
--- on the heady topic of " Television discharge question"

RH From: Ross Herbert

RH On Wed, 25 Aug 2004 02:05:03 -0400, "Tim Perry"
RH wrote:

RH |
RH |"Steve" wrote in message
RH |news | Hello,
|
| I have an old rear projection television that I would like to take
| apart and use the frame for another project. The television has not
| been plugged in since the year 2000. Do I still need to discharge
| capacitors even though it hasn't seen AC in 4 years?
RH |
RH |YES

RH And here I was thinking this was a troll......

RH Tell me, how can any charge storage device (capacitor) or aquadag
RH coating on a tube retain a charge when not having been powered up for
RH 4 years? Must be some magic new dielectric I haven't heard about, or
RH the air is awfully dry.


PURISTS!

The "YES" reply is in practice wrong, maybe even a little ignorant?
Realize, the crt glass has some leakage on the order of 10^14 ohms.
Say we have an aquadag capacitance of 0.005uF, then the time constant
is 500,000 seconds. Assuming 5 time constants for a nearly full
discharge this is 2,500,000 seconds or about 1 month. Clearly after 4
years there is practically no charge left.

A+s+i+m+o+v

.... High voltage can give a dangerously uncomfortable discharge.

"Ross Herbert" bravely wrote to "All" (26 Aug 04 04:31:20)
--- on the heady topic of " Television discharge question"

RH From: Ross Herbert

RH |Realize, the crt glass has some leakage on the order of 10^14 ohms.
RH |discharge this is 2,500,000 seconds or about 1 month. Clearly after 4
RH |years there is practically no charge left.

RH The actual time will depend on;

RH a) moisture content of the atmosphere
RH b) conductivity to chassis

RH In practical situations it won't take anywhere near this estimated
RH maximum to self discharge to a safe level.


Yes, even dry air is about 100 times more conductive than glass but
this neglects that the circuit wiring and anode boot insulate the air
path. The remaining path, assuming the focus divider is open circuit,
is via the HV rectifier but its leakage is of the same order as glass.
So then that could double the speed of the discharge. Okay, 2 weeks?!

A+s+i+m+o+v

.... I know flyback, ultor, and 47 other dangerous words.

Gentelman, question was not "theoretecly how long will a HV cap hold a
charge" it was "Do I still need to discharge
capacitors even though it hasn't seen AC in 4 years?" which i interpreted
as: "i don't know what i am doing so how do i do this safely?"

when working with old HV electronics never assume. tie a conductor to the
chassies and use it to touch everything.

dont even assume that it hasen't been plugged in in 4 years.

im recomending you follow basic safety procedures.

we can guess that 'probably' every thing is discharged and 'maybe' the
safety bleeders are intact.... but do you want to find out the hard way that
someone guessed wrong?

On Thu, 26 Aug 2004 21:37:40 -0400, "Tim Perry"
wrote:

Gentelman, question was not "theoretecly how long will a HV cap hold a
charge" it was "Do I still need to discharge
capacitors even though it hasn't seen AC in 4 years?" which i interpreted
as: "i don't know what i am doing so how do i do this safely?"

when working with old HV electronics never assume. tie a conductor to the
chassies and use it to touch everything.

Like a screwdriver w/clip lead to chassis? Or a test light? Any
recommendations for "discharge devices?"


__________________
Note: To reply, replace the word 'spam' embedded in return address with 'mail'.
N37.3 W122.0

I don't know the original question, but pretty much sitting overnight will
discharge the HV or filter caps. Sitting longer than a couple days=no charge
left.

"RonKZ650" wrote in message
...
I don't know the original question, but pretty much sitting overnight will
discharge the HV or filter caps. Sitting longer than a couple days=no
charge
left.

Usually a few minutes is enough to discharge it, however that's no reason
not to manually discharge it no matter how long it's been sitting. It may
have been off for 10 years, but like a gun, always treat it as if it's
loaded.